# Math Help - Newton-Raphson method

1. ## Newton-Raphson method

An equation f(x) = 0 has two roots in the interval between 0 and 8.
Give the value or a description of two starting values for which the newton raphson method will fail to converge to either root of the equation.

cheers

2. Originally Posted by sillylilly
An equation f(x) = 0 has two roots in the interval between 0 and 8.
Give the value or a description of two starting values for which the newton raphson method will fail to converge to either root of the equation.

cheers
Read practical considerations here: Newton's method - Wikipedia, the free encyclopedia

3. Yes I was just reading that before, only I don't understand how I can relate that directly to my problem?

4. If f(x)= 0 has two roots, then, by Rolle's theorem, there exist a value of x between those roots at which f' is 0. Quoting from the Wikipedia article mr. fantastic linked to
"4. It is clear from the formula for Newton's method that it will fail in cases where the derivative is zero. Similarly, when the derivative is close to zero, the tangent line is nearly horizontal and hence may "shoot" wildly past the desired root."